It is conventional to incorporate an absorbing compound or absorber, in particular, an ultraviolet ray absorber, in an image element to absorb light in a specific wavelength region. The ultraviolet ray absorbing light-insensitive layer is used, for example, in a silver halide photographic element, to control the spectral composition of light incident upon a photographic emulsion layer, and to absorb or to remove ultraviolet light produced by static discharge, which occurs when the surfaces of the photographic element come into contact during production or treatment processes. Electric charges are generated by friction between surfaces. When accumulation of static electricity by charging reaches a certain limiting value, atmospheric discharge occurs at a particular moment and a discharge spark fires at the same time. When the photographic element is exposed to light by discharging, static marks appear after development.
Different methods for incorporating an ultraviolet ray absorber into a photographic element have been described in, for example, U.S. Pat. Nos. 2,739,888, 3,215,530, 3,352,681, and 3,707,375. Oil soluble ultraviolet ray absorbers are incorporated into photographic elements by dissolving the oil soluble absorber in a high boiling point organic solvent, and mixing under high shear or turbulence the organic solvent with an aqueous medium, which may also contain a surfactant, in order to break the organic phase into submicron particles dispersed in the continuous aqueous phase. However, when such dispersions are used in a light-insensitive layer, the layer becomes soft and the mechanical properties of the layer are lowered. Furthermore, even if no high boiling solvent point is used, many ultraviolet absorbers themselves are liquid, and they therefore can have a detrimental effect on the mechanical properties of the layer and adhesion with the adjacent layer. In order to prevent these problems, a large amount of gelatin is used in the layer containing ultraviolet ray absorbers. When the ultraviolet ray absorbers are incorporated in the outermost layer of an photographic element, they often migrate and crystallize at the surface of the layer. Therefore, an additional overcoat layer is used to minimize this undesirable blooming phenomenon.
U.S. Pat. No. 5,110,717 describes a method of incorporating an ultraviolet ray absorbing compound or coupler by mechanically grinding a crystalline material to a desired particle size in a liquid that is not a solvent for the material, heating the crystalline particles to above their melting point, and cooling the melted particles to form amorphous particles.
Ultraviolet ray absorbing polymer particles obtained by polymerization of ultraviolet ray absorbing monomers are also known in the art. Different methods can be used to prepare such particles, for example, by emulsion polymerization or by dispersion of preformed ultraviolet ray absorbing polymers. Disadvantages of using such polymer particles are their high cost and poor light stability.
Another method of incorporating an ultraviolet ray absorber into a photographic element is by loading such an absorber into pre-formed latex particles as described in U.S. Pat. Nos. 4,199,363, 4,304,769, 4,247,627, and 4,368,258. In this process, a hydrophobe, such as an ultraviolet ray absorber, is first dissolved in a water miscible organic solvent and then blended with an aqueous latex. However, removing the water miscible solvent subsequent to loading requires large scale processing equipment and lengthy processing times, which increases the expenses of the incorporation procedure and the cost of the resulting products.
U.S. Pat. No. 5,536,628 describes a process for incorporating absorbers into a pre-formed latex polymer particle. In the process a polymer latex of known solids is heated with stirring to 70 to 80.degree. C. The absorbing compound is heated until it reaches its liquid state and is mixed with the polymer latex at high shear to generate an emulsion. The emulsion is then passed through a high energy homogenizer at least once to form an absorber impregnated latex polymer dispersion.
Processes described in U.S. Pat. Nos. 5,536,628, 4,199,363, 4,304,769, 4,247,627, and 4,368,258 can result in incomplete loading which leaves residual ultraviolet ray absorbers in the aqueous phase, which can then crystalllize or form large oil droplets during storage generating coating spot defects.
It is known in the art to use in photographic elements ultraviolet ray absorbers containing the following chemical structure unit: ##STR2## wherein R, may be the same or different, and each represents a hydrogen atom, a halogen atom, an alkyl, an aryl group having from 6 to 20 carbon atoms, an alkoxy group, an aryloxy, an alkylthio group, an arylthio group, an amine group, an alkylamino group, an arylamino group, an hydroxyl group, a cyano group, a nitro group, an acylamino group, a sulfonyl group, a sulfoamido group, an acyloxy group, or an oxycarbonyl group, or two neighboring R groups may form a 5 or 6-member ring by ring closure.
For example, the use of propyl 2-cyano-3-(4-methoxyphenyl)-2-propenoate in photographic elements is described in, for example, U.S. Pat. No. 5,288,598. However, such compounds are very prone to crystallization and therefore a large amount of high boiling solvent is needed for a stable dispersion.
Therefore, the foremost objective of the present invention is to provide an improved process for forming ultraviolet ray absorbing polymer particles in which a compound containing a chemical structure unit given by formula I is incorporated. Another object of the present invention is to provide an image element having at least one coated layer containing such ultraviolet ray absorbing polymer particles.